Global Positioning System

The Global Positioning System (GPS) is a satellite-based hyperbolic navigation system owned by the United States Space Force and operated by Mission Delta 31. It is one of the global navigation satellite systems (GNSS) that provide geolocation and time information to a GPS receiver anywhere on or near the Earth where signal quality permits.

GPS is very important because it helps people and machines know exactly where they are. This is useful for many things, like finding your way in a car, tracking where ships are on the ocean, or even helping farmers plant crops. It does not need the user to send any information out, and it works without phone or internet service, although those can make GPS even better.

Although the United States government created, controls, and maintains GPS, it is freely accessible to anyone with a GPS receiver. This means people all around the world can use it for many different purposes, from military operations to everyday activities like hiking or flying airplanes.

Overview

The GPS project began in 1973 by the U.S. Department of Defense. The first test satellite launched in 1978, and the full system of 24 satellites became operational in 1993. Originally, GPS was limited for civilian use to about 100 meters accuracy, but this was improved over time. By the year 2000, the accuracy was increased to about 5 meters, and newer satellites offer even better precision.

Today, many GPS devices, like those in smartphones, can be very accurate—sometimes within a few meters—especially when they use extra help from services like Wi-Fi positioning. As of March 2026, 21 satellites are broadcasting advanced signals, with plans to have all 24 by 2027.

History

The GPS project began in the United States in 1973 to improve upon earlier navigation systems. The U.S. Department of Defense created it, using 24 satellites, and it became fully operational in 1993. Originally for military use, civilian use was allowed starting in the 1980s. Key inventors include Roger L. Easton, Ivan A. Getting, Bradford Parkinson, and Gladys West.

GPS was developed from earlier systems like LORAN and the Decca Navigator System. It corrects for time differences predicted by Einstein’s theory of relativity, ensuring accurate positioning. The system was partly driven by the need to support the United States’ nuclear deterrent during the Cold War, especially for submarine-launched missiles.

Principles

The GPS satellites carry very stable atomic clocks that are synchronized with clocks on the ground. These clocks help determine the distance between the satellites and the ground stations. By knowing the exact time a signal was sent and when it was received, the system can calculate distances very accurately.

Each satellite broadcasts its own position and time information. A GPS receiver uses signals from at least four satellites to figure out its own location in three dimensions — like knowing where you are on Earth, how high up you are, and even the time. This works because the speed of the signals is constant, and by measuring small time differences, the receiver can pinpoint its exact spot. Modern satellites are being updated to provide even more accurate and reliable information for everyone using GPS.

Structure

The Global Positioning System (GPS) has three main parts: the space segment, the control segment, and the user segment. The U.S. Space Force manages the space and control parts. GPS satellites broadcast signals that help GPS receivers figure out their location and time.

The space segment includes 24 to 32 satellites orbiting Earth. These satellites travel in paths called orbits, making it easy to always have several in view from anywhere on Earth. The control segment tracks these satellites and makes sure their clocks are very accurate. The user segment includes all the people and devices that use GPS, from military tools to everyday gadgets like phones and car navigation systems. These devices use antennas and special clocks to pick up the satellite signals and show where they are.

Applications

Main article: GNSS applications

GPS is a very useful tool that helps people in many ways. Originally made for military use, it now has many civilian uses too.

GPS helps with many everyday activities. It provides very accurate time, which is important for things like banking, mobile phones, and even controlling power grids. People use GPS for finding locations, tracking movements, and many other tasks.

Some common uses of GPS include helping cars drive without a driver, letting people find their way with maps, and even in games like geocaching. It is also used in science to study the atmosphere and in weather forecasting.

Communication

Main article: GPS signals

GPS satellites send out special signals that tell receivers important information. These signals include the satellite’s location, the time, and the health of the whole system. The signals use two main frequencies that all satellites share. There are two types of signals: a public one for everyday users and a secret one for the military.

Each satellite sends a long message that takes about 12 and a half minutes to complete. This message is split into smaller parts that include the satellite’s exact position and general information about all satellites. GPS receivers use these signals to figure out their own location by listening to several satellites at once. The system uses special codes so receivers can tell each satellite’s signal apart, even though they all send on the same frequencies.

Navigation equations

Further information: GNSS positioning calculation

See also: Pseudorange

The Global Positioning System (GPS) uses signals from satellites to figure out where on Earth you are. A GPS receiver listens to messages from satellites that tell it where the satellites are and what time it is. By comparing the time it receives these messages to its own clock, the receiver can calculate how far away each satellite is.

To know your exact location, you need signals from at least four satellites. This is because the receiver’s own clock isn’t as precise as the clocks on the satellites. With four or more satellites, the receiver can figure out both where you are and how much its own clock is off. The more satellites you can receive signals from, the more accurate your location will be.

Accuracy enhancement and surveying

The Global Positioning System (GPS) can be improved for greater accuracy through techniques like differential GPS, which uses additional ground-based reference stations to correct satellite signals. This helps in precise surveying and mapping, allowing professionals to measure distances and positions with much higher accuracy. Such enhancements are especially useful in fields like land surveying, construction, and scientific research where exact locations matter.

Regulatory spectrum issues concerning GPS receivers

In the United States, GPS receivers follow rules set by the Federal Communications Commission. These rules say that GPS devices must work even if they get interference from other signals. GPS devices are made to avoid picking up signals from nearby frequency bands.

The Federal Communications Commission has allowed a company called LightSquared to use frequencies close to those used by GPS. This caused worries that LightSquared’s signals might interfere with GPS. In 2012, the FCC decided to stop LightSquared’s plan because it could disturb GPS signals. This decision was made after talks with other government groups that use GPS, like the United States Defense Department and Federal Aviation Administration.

Similar systems

Main article: Satellite navigation

After the United States created GPS, other countries made their own systems to help people find their way. Russia made GLONASS, which now works all around the world. China created the BeiDou system, which finished growing in 2020. Europe built Galileo, which started in 2016 and keeps growing. Japan has a system called QZSS to make GPS even better in Asia and the Pacific. India also has its own system named NavIC.

Backup system

If space weather or an attack happens to the GPS satellites, the United States does not have a land-based system to take its place. This could cause big problems for the U.S. economy. A system called eLoran has been suggested as a backup, but it is not yet approved or funded.

China still uses a system called LORAN-C, and Russia has a similar system called CHAYKA ("Seagull").